Technical Field
The present invention relates to a prismatic secondary battery having a current disconnection mechanism and a battery pack which uses the prismatic secondary battery.
Related Art
Secondary batteries such as lithium ion secondary batteries are used in driving power sources of electric vehicles (EV) and hybrid electric vehicles (HEV, PHEV), and stationary storage battery systems used for inhibiting output fluctuation of solar light power generation, wind power generation, or the like, or for peak shift of system power for storage of electric power during the night and usage of the power during daytime. In the EV, HEV, or PHEV usage or in a stationary storage battery system, properties of high capacity and high power are desired. Therefore, a size of the individual battery is increased, and a large number of batteries are connected in series or in parallel for use.
For the batteries used for these usages, in particular, when a non-aqueous electrolytic secondary battery is used, a material having a very high reactivity is used, and thus, a degree of safety which is much higher compared to the secondary battery used in small-size, portable devices is required. Because of this, in prismatic secondary batteries used in the above-described usages, a current disconnection mechanism that disconnects electric connection between an external terminal and an electrode structure when a pressure in a battery outer structure is increased is provided, as described in, for example, JP 2008-66254 A, JP 2008-66255 A, JP 2010-212034 A, and JP 2013-175428 A.
The present inventors have found, in development of high-power, high-capacity battery packs, that in a battery pack in which the number of prismatic secondary batteries connected in series is increased and a total voltage of the battery pack is greater than or equal to 100 V, there is a possibility that, after the current disconnection mechanism is activated, spark may be generated inside the prismatic secondary battery, which may then damage the outer structure or the like of the prismatic secondary battery. The present invention resolves such a problem, and in particular, provides a prismatic secondary battery in which damage to battery constituting components, in particular, the outer structure of the battery, by the spark or the like after the current disconnection mechanism is activated, is prevented.
The present inventors have searched for the cause of the spark generated inside the battery after the current disconnection mechanism is activated, and found that the cause of the spark is as follows.
When the prismatic secondary battery is excessively charged, gas is generated inside the battery, and an inner pressure of the battery is increased. The current disconnection mechanism is then activated, and the electric connection between a first conductive member and a second conductive member of the current disconnection mechanism is cut off. Then, when a large voltage is applied to the prismatic secondary battery in a state where the electrolytic solution is adhered to a surface of an insulation member of the current disconnection mechanism, a current flows in a route from the first conductive member of the current disconnection mechanism, to electrolytic solution on the surface of the insulation member of the current disconnection mechanism, and further to the second conductive member of the current disconnection mechanism. Because the electrical resistance of this route is very high, when current flows in this route, heat is generated, the temperature of the insulation member surface is further increased by electrolysis of the electrolytic solution, the surface of the insulation member or the electrolytic solution existing on the surface of the insulation member is carbonized (in particular, carbonization of the surface of the insulation member has significant influence), and the route becomes a conductive route of a lower resistance. A spark is then generated partway in the conductive route.